function [F_f,F_f_c] = face_flux(U)
%求各面的流通量
global own nei num U_inlet b c_s
F_f=zeros(own(1),1);
F_f_c=zeros(num,num);
for i=1:nei(1)
    U_f=U(own(i+1),:)/2+U(nei(i+1),:)/2;
    F_f(i)=U_f*c_s(i,:)';
    F_f_c(own(i+1),nei(i+1))=U_f*c_s(i,:)';
    F_f_c(nei(i+1),own(i+1))=-U_f*c_s(i,:)';
end
%引入边界流通量
for i=1:b.in(1)
    F_f(i+b.in(2)-1)=U_inlet*c_s(i+b.in(2)-1,:)';
end
for i=1:b.out(1)
    l=own(i+b.out(2));
    F_f(i+b.out(2)-1)=U(l,:)*c_s(i+b.out(2)-1,:)';
end
for i=1:b.sym1(1)
    F_f(i+b.sym1(2)-1)=0;
end
for i=1:b.sym2(1)
    F_f(i+b.sym2(2)-1)=0;
end   
end